Editor's note: Maya MacGuineas is the president of the bipartisan Committee for a Responsible Federal Budget and the director of the fiscal policy program at the New America Foundation.

Washington (CNN) -- When the president unveils his 2011 budget next week, he will propose capping "non-security" discretionary spending at its current level of about $450 billion for three years, saving roughly $250 billion over ten years.

The freeze does not include defense, veterans' affairs, homeland security and some international programs.

Let's start by putting these numbers in context. The Congressional Budget Office's new baseline numbers show that deficits will be $6 trillion over the next decade -- under highly unlikely assumptions that Congress will stay true to current law, where the tax cuts and other popular policies expire -- or more than $12 trillion under more likely assumptions.

So $250 billion, while obviously a large number, is a very small share of the amount Congress is poised to borrow -- and add to the debt -- in the coming decade.

It would be fair, then, to say that this is a baby step -- OK, it's a teeny-weeny tiptoe of a step -- in the right direction. But there have been so many steps in the wrong direction in recent years, such as extending tax cuts, that anything that it can legitimately be argued would help bring down future deficits should be heralded as an important move.

And frankly, it is a courageous one too for this administration; there are going to be an awful lot of members of the president's own party who are none too happy with the plan.

But remember, the president's budget for the fiscal year that begins in October isn't actually a law. It is more like a polite suggestion to Congress. Given that Democrats run the House and Senate, they won't declare the budget dead on arrival, as so often happens when the budget season begins with a president of one party delivering his budget to a Congress run by the other.

But in this highly charged election year, where legislators will talk about being tough on spending but not necessarily back that claim with real spending cuts, it will be extremely difficult to get them to stick to this freeze.

Therefore, the president is going to have to back up his promise with more than words for it to be seen as credible. What it needs is teeth.

First, he should promise to veto any appropriations bills that exceed the limits he has put forward for spending. Otherwise, there's little question that appropriators will find all sorts of ways to bump up spending beyond what he has proposed -- everything from budget gimmicks to simply ignoring his proposal.

If he chooses to look the other way, the spending freeze will prove to be little more than a cynical political talking point at a time when real action is needed. Shepherding the budget from blueprint to law is part of the heavy lifting the president will have to lead on.

Second, he should support statutory spending caps that enforce his limits. This is an idea that is gaining momentum in the Senate and House, and it is the ideal companion piece to his suggested freeze. From Sen. Jeff Sessions, R-Alabama, to Sen. Evan Bayh, D-Indiana, to Sen. John McCain, R-Arizona, he need not look far to find a host of good ideas.

Finally, there is the issue of the rest of the budget. Non-security is only a small sliver of discretionary spending, and discretionary is only a small sliver of total spending. All told, we are talking about less than one-sixth of the budget. It would be more sensible to cap all discretionary spending and force policymakers to make tradeoffs between defense and other security parts of the budget as well, not just within the relatively small non-security category.

And then there are still the big enchiladas -- Social Security, health spending, and taxes -- to be dealt with. When this fight gets going, remember, it will only be working its way down from the tip of the iceberg.

Nonetheless, a discretionary freeze is a sensible first step. Let's hope when the rest of the budget is released on Monday, it will take that first tiny sensible step much further.